In UMTS (Universal Mobile Telecommunications System) networks, for the purpose of improving spectral efficiency and further improving data rates, by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), it is performed exploiting maximum features of the system based on W-CDMA (Wideband Code Division Multiple Access). For the UMTS network, for the purpose of further increasing high-speed data rates, providing low delay and the like, Long Term Evolution (LTE) has been studied.
In the 3G system, a fixed band of 5 MHz is substantially used, and it is possible to achieve transmission rates of approximately maximum 2 Mbps in downlink. Meanwhile, in the LTE-scheme system, using variable bands ranging from 1.4 MHz to 20 MHz, it is possible to achieve transmission rates of maximum 300 Mbps in downlink and about 75 Mbps in uplink. Further, in the UMTS network, for the purpose of further increasing the wide-band and high speed, successor systems to LTE have been studied (for example, LTE Advanced (LTE-A)). For example, in LTE-A, it is scheduled to increase 20 MHz that is the maximum system band in LTE specifications to about 100 MHz. Further, it is scheduled to increase four antennas that are the maximum number of transmission antennas in LTE specification to eight antennas.
Moreover, in the LTE-scheme system, MIMO (Multi Input Multi Output) systems are proposed as radio communication techniques for transmitting and receiving data using a plurality of antennas and improving a data rate (spectral efficiency) (for example, see Non-patent Document 1). In the MIMO systems, Space Division Multiplexing (SDM) techniques are used in which using a plurality of transmission/reception antennas, a plurality of different transmission information sequences is transmitted at the same time with the same frequency. The receiver side exploits the fact that different fading variations occur in between transmission and reception antennas, and divides the simultaneously-transmitted information sequences to detect, and it is thereby possible to increase the data rate (spectral efficiency).
In such a MIMO system, since it is necessary to consider Multiple Access Interference (MAI), it is required to suitably estimate a state of a channel that is a propagation path.